Method of making cathodes



Aug; 5, 1,947.

Ne/d

Weld/'n w. w. EITEL rAL METHOD OF MAKING CATHODES Filed Aug. 24, 1942 INVENTORS W. ETEL ive/ding fab THEIR ATI'ORN l MLL/A BY Mx Loue-IH Patented Aug`.-5, 1947 A METHQD F MAKING CATHODES William W. Eitel, Salt Lake City. Utah, and Jack A. McCullough, Millbne, Calif., assgnors to Eitel-McCullough, Inc., San Bruno, Calif., al corporation of California.

Application August 24, 1942,Serial No. 456,127

(Cl. L-71.6)

4 Claims. 1

Our invention relates to the manufacture of cathode structures for electronic tubes.

It is among the objects of our invention to provide a method of making a helical-type filamentary cathode, whereby distortion of the filament during welding is largely eliminated.

Another object is to provide an improved method of welding a filament to a lead, producing a clean weld having superior mechanical strength.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims,

Referring to the drawing:

Figure 1 is an exploded elevational view showing. a -filament and associated parts prior to engagement of the upper welding disk.

Figure 2 is a plan View looking down at the top of the filament before applying the welding disk, illustrating the clearance between 4the end coil and lead prior to welding.

tice of making lamentary cathodes of this character. Both leads are preferably of tungsten.

Helical filament 6, preferably of thoriated tungsten, is provided with a depending lower end 'l arranged to lie alongside lead 3 when the filament is centered about lead 2. The upper end of the filament is formed with a reduced coil 8 aligned with the axis and sized to loosely encircle the upper portions of coaxial lead 2. Three convolutions are shown in coil 8, but it is understood that one or more may be present in the coil, the important thing being that the convolutions are spaced from lead 2 to give freedom of movement to this end of the filament. See Figure 2.

The filament is temporarily held by a jig comprising a longitudinally split body having a pair Figure 3 is a vertical sectional view showing the cathode structure within a bell jar ready for welding.

Figure 4 is a side elevational view of the welded filament.

In terms of broad inclusion, our method of making a cathode structure comprises forming a helical filament with a reduced end coil sized to loosely encircle a lead, positioning the filament with the coil embracing the lead, fixing the other end of the filament, and then welding said coil to the lead. In making our structure we preferably first seal a pair of cathode leads to a stern; then x the lower end of the filament by welding to one of the leads; and then weld the coil at the upper end of the filament to the other lead. Welding is preferably effected by an electric arc in an atmosphere of hydrogen, after which the structure is heated in a hydrogen yatmosphere by passing current through the iilament.

In greater detail, and referring to the drawing, we rst nx a pair of leads 2 and 3 to a support, as by the usual practice of sealing them to a stem 4 of the envelope which encloses the cathode in the nal tube. Short lead 3 is arranged to terminate adjacent the lower end of a helical filamentiy while longer lead 2 is disposed coaxially with the' cathode to terminate adjacent the upper end of the filament, in accordance with ordinary pracof half-sections 9 gripped by jaws II of a suitable clamp, and having an axialbore through which the helical portion of the filament extends. The diameter of the bore is preferably slightly larger than the outside diameter of the helix so that there is a small clearancejust enough to prevent binding of the parts and toallow some freedom of movement. The jig is centered by spacing lugs I2 engaging coaxial lead 2 between the convolutions of the helix. hold the filament in proper axial position. The free play at the top provided by the clearance between coil 3 and lead 2 allows the helix to be centered without putting stress in the wire, which stress would cause distortion after the jig was removed.

In assembling the parts, a tab I3 of metal flux is first spot welded to lead 3. Any suitable material, such as platinum, which liuxes or welds readily with both the lament and lead may be used. The filament is then mounted by the jig on center lead 2 with its depending end l against tab I3 on lead 3. Another piece of metal flux is also applied to the junction between coil 8 and the center lead. This piece preferably comprises an apertured disk I4 of molybdenum engaged over the end of lead 2 above coil 8. The disk is thus held by the lead ready for 'welding and allows the structure to be elevated into a bell jar without the disk falling off.

These lugs also of the filament is preferably first brought into the arc for welding. The heat causes piece I3 to flow or flux into intimate contact with the Illa'- ment and lead, producing weld i9 shown in Figure 4.

One of the most diicult problems in mounting a helical illament is that the heat coincident with welding causes distortion of the filament. This distortion is largely eliminated in our procedure because tt illament is free to turn under torque stresses set up in the helix due to expansion of the wire under heat. Loose coil 8 at the top permits the filament to rotate about lead 2 without destroying the coaxial alignment. After making weld I9 the structure is lowered to place the upper juncture in the are. The

molybdenum flows down over the convolutions' of coil B, filling the space between the coil and lead, and welding the parts together without altering the alignment of the filament. The final weld is a smooth bead 2i enveloping the coil as shown in Figure 4. Arc Welding in a hydrogen atmosphere results in clean welds, free of oxides and other contamination which, if present, are difficult to eliminate and adversely aiiect the operation of a tube.

Upon completion of the upper Weld the struc* ture is Withdrawn from the bell jar and the jig is removed. In order to further improve the welded joints we preferably again elevate the structure into a hydrogen filled bei and heat the cathode to incandescence by pas ng current through filament. This causes further knitting of the welding material and produces smooth, tight joints.

We claim:

1. The method of making a cathode structure, which comprises forming a helical iiazeicnt with a reduced coil at one end sited to loosely encircle a lead, positioning the filament with said coil embracing the lead, welding the other end ci the filament to another lead, applying to the juno ture at said coil a piece 0I metal weldable with the filament and said first lead, and then sub-- jecting th juncture to welding heat.

2. The method of making e cathode structure which comprises forming a helical iliament with a reduced coil at its upper end sized to iooseiy encircle a first lead, positioning the filament with said coll embracing the lead and 'with its lower end adjacent another lead, weldingY the lower end of the illament to said other lead. engaging over the upper end of the rst lead an apertured piece of metal weldafble with the filament and the tlrst lead, and subjecting the juncture at the upper end oi the filament to welding heat.

3. The method oi making a cathode structure, which comprises fixing a pair of leads to a support, forming a helical filament with a reduced coil at its upper end sized to loosely encircle a rst of said leads, positioning the illament with said coll embracing the first lead and with its lower end adjacent a second lead, welding the lower end to the second lead, and welding the coil to said irst lead.

4. The method of making a cathode structure, which comprises fixing a pair of leads to a support, forming a helical filament with one end portion directed toward the helical axis so as to lie in close proximity to such axis, positioning a first lead of said pair within the helix of the illament in substantial alignment with the helical axis thereof and contiguous to the inwardly directed end portion of the filament, positioning the second lead of said pair adjacent the oppo site end portion of said filament, welding said last named end portion of said filament lto the adjacent second lead, and thereafter welding said first named end portion of said filament to said first lead.

WILLIAM W. EITEL. JACK A. MCCULLOUGH.

REFERENCES CITED The following references are of record in the tile oi this patent:

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